Field of the Invention
The invention relates to the field of solar-thermal power generation, and more particularly to a solar-thermal complementary power generation device/system comprising solar trough thermal collector tubes as well as a power generation method using the same.
Description of the Related Art
Typical trough solar thermal power generation systems employ a turbine to drive the motor and employ water vapor as a working medium. In general, the evacuated solar collector tubes of the trough solar thermal power generation systems employ conduction oil (or melted salt) to collect solar energy, and the heated conduction oil (or melted salt) heats water to produce steam to drive the turbine for power generation. FIG. 1 shows an evacuated solar collector tube module, which includes a parabolic trough reflector 1b1 and an evacuated solar collector tube disposed at the focal point of the parabolic trough reflector. The evacuated solar collector tube includes a glass tube 1b2 and an absorption tube 1b3 coated with a heat absorption layer. The glass tube is sleeved on the absorption tube, and a space between the glass tube 1b2 and the absorption tube 1b3 is vacuum.
The above trough solar thermal power generation systems includes at least the following two disadvantages. First, the solar energy is subject to the weather conditions, so it is unstable and discontinuous. The conduction oil (or melted salt) can store thermal energy, thereby offsetting the influence of the weather. Second, the trough solar thermal power generation systems employ evacuated solar collector tubes, which cannot be adapted to the physical properties of water, when water is heated to certain temperatures and pressures by solar energy, the tubes may burst.
That is because the solar energy concentrated by the trough reflector always heats the side of the evacuated solar collector tube close to the parabolic trough reflector 1b1 (as shown in FIG. 1, the lower part of the glass tube 1b2), while the opposite side, that is, the upper part of the glass tube in FIG. 1, will never receive concentrated sunlight, and the convergence ratio thereof is 80:1. As a result, the instantaneous temperature difference between the upper and lower part is up to more than 300° C. The space between the glass tube 1b2 and the absorption tube 1b3 is vacuum. If the absorption tube 1b3 is filled with conduction oil (or melted salt), the good heat conductivity of the liquid medium can quickly equalize the temperature of the absorption tube 1b3, thereby preventing the occurrence of the large temperature difference and the formation of internal stress. If the absorption tube 1b3 is filled with water, when the water temperature exceeds 100° C., water vapor is produced and floated on the upper part of the horizontally placed long evacuated solar collector tube, and the lower part thereof is liquid water. The heat conductivity difference of the water vapor and the liquid water is huge, which inevitably causes the huge temperature difference of the upper and lower parts of the evacuated solar collector tube, and due to the heat expansion and cold contraction of the tubes, large internal stress is produced, and thus the evacuated solar collector tube tends to burst.